IBM created the wafer processing technology and concepts more than 45 years ago that would later enable what we call Wafer Level Packaging. With its introduction of the Controlled Collapse Chip Connect (C4) solder bumping process for use in its Solid Logic Technology package, it paved the way for the larger solder bump technology that enabled die to be mounted directly on circuit boards using standard surface mount equipment, and standard pitch circuit board technologies. Over ten years ago, Wafer Level Chip Scale Packaging (WLCSP) came into volume production, with all of the “packaging” done while still in wafer form. It began slowly, with very small packages having solderball counts of 2–6 I/Os. Over the years, the production volumes have grown, and so has the I/O count. Much of the industry still perceives WLCSPs as limited to low I/O count simple applications. However, within the last few years, there have been growing demands for WLCSP packages with I/O counts of 300 and greater, and with higher levels of complexity.
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